With a vegetable peeler, remove any fibrous strings from the fennel or celery stalks. Slice the vegetables lengthwise into 1/4-inch slices. Cut the slices crosswise into inch-dice.

In a 10-inch skillet, over moderate heat, combine the olive oil and onion. Cover and cook, stirring occasionally, until the onion is translucent, about 5 minutes. Add 3/4 of the diced fennel or celery, the water, and salt. For fennel, add 1/2 teaspoon fennel seed; for celery, add 1 teaspoon of the seeds. Bring to a boil, reduce the heat, cover and simmer until the vegetables are tender and most of the liquid has evaporated, about 20 minutes. Stir in the reserved fennel or celery, the olives, and lemon zest. Season with salt and pepper to taste and serve at once.

Sally Schneider is the founder of The Improvised Life, a lifestyle blog that inspires you to devise, invent, create, make it up as you go along, from design and cooking to cultivating the creative spirit. It's been called a "zeitgeist-perfect website." She is a regular contributor to public radio's The Splendid Table and the author of the best-selling cookbooks The Improvisational Cookand A New Way to Cook, which was recently named one of the best books of the decade by The Guardian. She has won numerous awards, including four James Beard awards, for her books and magazine writing.

Sally has worked as a journalist, editor, stylist, lecturer, restaurant chef, teacher, and small-space consultant, and once wrangled 600 live snails for the photographer Irving Penn. Her varied work has been the laboratory for the themes she writes and lectures about: improvising as an essential operating principle; cultivating resourcefulness and your inner artist; design, style, and food; and anything that is cost-effective, resourceful, and outside the box.